Abstract

Abstract

Fragipans or “X” horizons have been recognized in highly weathered soils of southern Indiana for more than 30 years. They occur at depths of 2 to 4 feet, and are most common in imperfectly and moderately well-drained soils.

Profiles of three highly weathered soils of the residual area of southern Indiana were selected for study. A fourth profile which did not have a fragipan, but was formed from similar parent material was sampled for comparison. Detailed chemical and mineralogical studies were made on the nonfragipan profile and one of the fragipan profiles.

Each of the soils with fragipans had a pH of 4.5 or less in the B horizon. The profile without a fragipan had a minimum pH of 5.6. Horizons of one fragipan profile were shown to contain iron oxide as a cementing agent. The clay of the fragipan was found to be lower in montmorillonite than the clay from comparable horizons of the profile without a fragipan. Only a small portion of this montmorillonite from the fragipan was capable of expansion without sample pretreatment.

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